Craig Harvey, operations chief of the L.A. County coroner's office, said the tests will take four to six weeks to complete, at which time he anticipates being able to issue a final cause of death.

Harvey added that the coroner found "no indication of any foul play on the body of Mr. Jackson."

Watch "Michael Jackson: The Man and His Music" on a special edition of "20/20" TONIGHT at 9 p.m. ET.

But according to a senior law enforcement official briefed on the initial investigation of Jackson's death, it's probable drugs played a part. He told ABC News that Jackson was "heavily addicted" to the powerful pain killer Oxycontin and received "daily doses" of it and of another pain killer, Demerol.

The Los Angeles police were told Jackson received an injection of Demerol one hour before his death, the official added.

Los Angeles Police Deputy Chief Charlie Beck said Friday in a press conference that the robbery/homicide division has been in contact with Conrad R. Murray, the doctor present at Jackson's home when 911 was alerted.

Jackson's Autopsy Results: Why the Delay?

Delays of several weeks between the death of a celebrity and the release of their final autopsy report are not uncommon, as seen in the past.

There are many factors that can contribute to this delay, not the least of which is the fact that while preliminary tests of blood and urine can often be performed quickly, other processes can take more time.

"The preliminary results will be available early -- within 48 hours -- for many substances; however, other levels may be sent to other laboratories with required analytical capabilities that will need time to run specific assays," said Dr. Christopher Holstege, director of medical toxicology and the University of Virginia in Charlottesville. "That could take weeks depending on the priority that is being placed on those samples."

Teasing out the exact levels of each of the possible drugs involved could also require more extensive testing. In Jackson's case, because pain medications may have been involved, the possibility that the interactions between multiple drugs is a distinct one, noted Dr. Paul Christo, director of the Pain Treatment Center at Johns Hopkins Hospital in Baltimore.

"If you are on multiple medications ... if you combine these medications and take any one in excess, then that can tip you over the point where you lose the ability to breathe well," Christo said. He added that if Jackson happened to be taking alcohol at the time as well, it could magnify this effect.

Those Close to Jackson Knew He Wasn't Well

Like law enforcement officials, Jackson family attorney Brian Oxman suspects drugs led to his death. Oxman claims Jackson's family tried "many times" to get Jackson off the many prescription painkillers he took for years. He confirmed that a doctor was summoned to Jackson's home the night before he died.

"I don't want to jump to conclusions, and I don't want to point fingers," Oxman said. "We don't know what Michael Jackson perished from, but what I do fear is that it was the medications."

Oxman, who was at the hospital with the Jackson family when he died, said Jackson first started taking pain medication after his hair caught fire during the filming of a Pepsi commercial in the early 1980s. The drugs subsequently became a regular part of his life when Jackson later fell off a stage and suffered a broken leg and a cracked vertebrae.

"I spoke to family members. I said if this situation arises where Michael perishes because of these medications ... I will not hold my tongue," Oxman said. "I will speak out and I will speak out loud about the overmedication of Michael Jackson."

Oxman noted that the stress of Jackson's upcoming tour may have put him under tremendous pressure.

"Michael was rehearsing and working extremely hard," he said. "I think he was in discomfort because he was working so very hard."

Jackson's 2005 trial on child molestation charges also created a burden on the star that Oxman said changed him for good.

"When I knew him during the trial, he was extraordinarily frail physically and emotionally unstable -- a 45-year-old 12-year-old," he told ABC News. "So thin and gaunt -- it was almost impossible for me to imagine him going through a grueling trial proceeding."

Brafman added Jackson "didn't strike me as someone who could survive much longer."

Family friend Mark Lester, also the godfather of Jackson's three children, said he never saw any signs of Jackson's use of prescription pain medication or that he was in ill health in the days leading up to his death.

"There was no indication of anything other than Michael focusing his everything on this set of concerts," he said from London this morning.

Lester said that, if called to do so, he would absolutely step up to care for Jackson's children, Prince Michael I, Paris and Prince Michael II, but that there would be no shortage of people willing and able to take them in.

"Michael has a large family," he said. "I'm sure the children will be well looked after."

Lester said he was unsure if the children had been told about their father's death.

"The kids were everything to Michael. They were his whole life," he said. "He was a very active and involved father."

Jackson's Sudden Cardiac Arrest

The Los Angeles Fire Department was called to Jackson's residence at 12:26 p.m. PT Thursday. Paramedics performed CPR on Jackson, who was not breathing when they arrived at his home. He was rushed to L.A. Medical Center, six miles from his home.

Oxman said there was complete pandemonium at the hospital where Jackson was pronounced dead after doctors worked on him for more than an hour.

"Nobody knew what was happening," he said. "We couldn't even speak."

While Jackson's family and friends were inside the hospital trying to understand a life without Jackson, fans began to gather outside.

"It was one of the most eerie experiences of my life at the hospital," Oxman said. "The fans gathered, there were thousands of them. To hear 'Billie Jean' and 'Beat It' echo off the walls of the hospital" was surreal.

Jackson's older brother, Jermaine Jackson, 54, told the media that emergency room doctors worked to resuscitate the pop star for one hour after he arrived at the hospital.

"They were unsuccessful," he said. Michael Jackson's personal physician was with the singer when he collapsed at his home and worked to revive him.

"The word he spoke with the greatest emphasis was the 'More!' that he exclaimed when I asked if he could still do all his famous moves and hit all those notes at the age of 50," said Connelly of his August 2008 phone interview with Jackson.

Connelly asked Jackson if he had received his AARP membership, a question that garnered a laugh from the star.

"In an all-too-short life that in so many ways was filled with enigmatic emotions, or troubling ones, his laugh sounded fresh, clear and altogether genuine," said Connelly. "If only there had been more of those."

Jackson's death came less than a month before the start of a scheduled series of so-called comeback concerts. From July 13 to March 6, 2010, Jackson was scheduled to perform 50 soldout concerts at London's O2 Arena.

Fans last heard from Jackson during a press conference in London last March, where he assured about 2,000 fans that his upcoming concert would be his "final curtain call."

"I just want to say that these will be my final show performances in London," he said to the screaming crowd. "This will be it. When I say this is it, this will be it."

Groomed for Stardom

Born Michael Joseph Jackson in Gary, Ind., in 1958, the King of Pop was the fifth of nine children of Joe and Katherine Jackson. Both parents instilled a love of music early in their children's lives: Katherine taught them folk music while Joe, a budding guitarist, managed them and molded their musical work ethic.

The brothers were discovered by Motown singers Diana Ross and Gladys Knight and pianist Billy Taylor after a performance at the Apollo Theater in New York's Harlem. Motown Records founder Berry Gordy would soon sign them to a contract.

Gordy's investment paid off: The Jackson 5 broke through to national stardom in 1969-70 with four consecutive hit songs. Energetic, dancing prepubescent Michael was the standout of the group.

"I saw so much of myself as a child in Michael," Diana Ross told a reporter in 1970. "He was performing all the time. That's the way I was. He could be my son."

From 'Thriller' to Oddball

While still a member of the Jackson 5, Jackson made his first solo album, "Got to Be There," in 1972. He began to define himself as a solo artist with the 1979 release of "Off the Wall." However, he became an international phenomenon when "Thriller" sold 16 million copies worldwide in 1983.

Propelled by songs such as "Beat It" and "Billie Jean," as well as his unique "moonwalk" dance and his music videos, "Thriller" became the second-greatest-selling album of all time. He appeared in magazines worldwide as fans imitated the moonwalk and wore the single sequined glove and high-water pants he popularized at one point. Not even an accident during the filming of a Pepsi commercial in which his hair caught fire could stop Jackson from becoming a pop icon.

After "Thriller," Jackson's physical appearance began to change drastically. The headlines didn't focus on it at the time, but when Jackson released "Bad" in 1987, he appeared to have much more feminine facial features.

His complexion, once brown, morphed into a pasty white. His once-flat nose was reshaped, his cheekbones were more defined and his hair -- once a Jeri-Curled Afro -- was straightened.

Jackson denied having extensive plastic surgery and blamed his change in skin tone on vitiligo, a pigment disorder.

Then his behavior appeared to become increasingly odd, with reports that he slept in a hyperbaric chamber and tried to buy the Elephant Man's bones. In 1991, around the time of the release of "Dangerous," he began calling himself "The King of Pop" with no explanation but in apparent homage to his influence and his record-breaking success as an artist. However, Jackson was still recognized primarily for his talent and perhaps perceived as benevolently eccentric.

The Child Molestation Cloud and Trial

But Jackson's career took a darker turn in 1993 when a 12-year-old boy accused him of molestation. Jackson always denied any wrongdoing and was never charged in that case. Santa Barbara County, Calif., prosecutors decided not to pursue a criminal case when they said the alleged victim refused to testify.
Jackson ultimately settled a civil suit filed by the boy's family for a reported $20 million. But suspicions of child molestation continued to follow Jackson and he went on trial in 2005 after a boy who appeared with him in "Living With Michael Jackson" accused him of wrongdoing.

Jackson raised eyebrows during the documentary when he talked about his fondness for having innocent sleepovers with children at Neverland. While holding hands with his accuser in his criminal case, he said, "Why can't you share your bed? The most loving thing to do is to share your bed with someone."

Jackson insisted the practice was innocent and involved nothing of a sexual nature. "I give them hot milk, you know, we have cookies. It's very charming. It's very sweet. It's what the whole world should do."

However, Santa Barbara County prosecutors did not think the practice was so innocent, and the documentary led to a raid of Neverland and Jackson's arrest for child molestation.

A California jury of eight women and four men acquitted Jackson of molestation, attempted molestation, playing minors with liquor, and conspiracy stemming from an alleged attempt to hold hostage the accuser and his family at Neverland after the documentary aired. Jackson's defense argued that the alleged victim and his family made up the allegations in an attempt to get money.

Clouded Legacy

In the last decades of his life, headlines focused less on Jackson's music and more on his bizarre behavior, marriages and child molestation suspicions. His record sales dwindled. Jackson's last studio album, 2001's "Invincible," sold just more than 2 million albums (8 million worldwide) -- successful to most artists but a disappointment for the "King of Pop." Despite hitting the top of the music charts worldwide, Jackson hadn't had a No. 1 single in the United States since 1995's "You Are Not Alone."

Jackson was married briefly to Lisa Marie Presley, daughter of Elvis. A three-year marriage to his dermatology nurse, Debbie Rowe, followed, and she bore him a son and a daughter, Prince Michael I and Paris. Jackson had a third child, Prince Michael II, by another, unidentified woman in 2002.

Jackson stirred outrage when he dangled a then-infant Prince Michael II from the balcony of a Berlin hotel in November 2002. He denied purposely endangering his child, and German authorities decided not to pursue charges.

There have been reports of financial trouble ever since his 2005 child molestation trial. Last year, he was forced to sell his famous Neverland ranch. In April, 2,000 items from his Neverland estate will be up for auction at the Beverly Hills Hilton. The entire sale is estimated to bring in between $1.5 million and $3 million, according to Darren Julien, the head of Julien's Auctions, which is conducting the sale.

It remains to seen whether Jackson will be remembered primarily for his music or the child molestation scandals that followed him. Despite his acquittal, some critics -- and former fans -- had lingering questions about his friendships with young boys that lasted to his death.

Though he dubbed himself "The King of Pop," Jackson also believed he was a modern-day version of Peter Pan, saying that he never had a childhood. He said he built his Neverland ranch not only as a refuge for himself but for children -- especially those who are ill or less fortunate -- to enjoy.

Jackson's fans and detractors will always debate his public persona, but his legacy in the music industry is undeniable. He won 18 Grammys in his career and was inducted into the Rock and Roll Hall of Fame twice, as both a solo artist and member of the Jackson 5. Jackson's revolutionary videos for "Thriller," "Beat It" and "Billie Jean" put MTV on the map. His influence is found in some of today's chart-toppers, such as Usher, Justin Timberlake and Alicia Keys, who say they grew up listening to him. Jackson was also a member of the Songwriters Hall of Fame.